Synergizing rice productivity sustainability through an integrated water-nitrogen management strategy based on multi-objective optimization.

Despite advances in rice water and nitrogen (N) management, previous studies still fail to quantitatively balance economic benefit and environmental cost on the basis of high yield, and lack robust N diagnostic thresholds for rice production. In a three-year field experiment, treatments comprised two irrigation regimes, conventional irrigation (CI) and alternate wetting and drying (AWD), and four N rates (0, 180, 270, and 360 kg N ha-1). Results suggest that AWD significantly outperformed CI, enhancing grain yield (12.39%-16.02%), agronomic N efficiency (12.27%-22.30%), and economic benefits (27.36%-38.07%), while mitigating global warming potential (GWP) by 25.90%-29.59%. Distinctively, this is the first study to incorporate an inverse normalization-based trade-off model between yield, economic benefit, and GWP under AWD in the lower reaches of the Yangtze River, identifying 235.37-273.09 kg N ha-1 as the optimal N range in this region. Compared to the rate for maximum yield (311.12 kg N ha-1), this optimized N range maximized economic profitability and N use efficiency while reducing GWP, with a negligible yield penalty of only 0.60%-2.38%. Furthermore, we establish quantitative diagnostic thresholds for dry matter and N accumulation at key growth stages, providing a robust tool for in-season N management in this region. Unlike traditional leaf color diagnostics, these thresholds are quantitative field indicators that can directly guide in-season topdressing decisions. This integrated water-N management strategy based on multi-objective optimization provides a viable pathway for the sustainable intensification of rice systems.